An endless track chain used in tractors, excavators and other track-type machines includes links, track pin bushings, track pins, and shoes. Each section of the track includes a pair of links fastened together with a track pin bushing and a track pin. The bushing couples one pair of links while the track pin fits inside the bushing to hold the next pair of links along the endless track chain. A track shoe is bolted to each connected pair of links to support the machine and provide traction. The design of the shoes may be determined by the environment of intended use (e.g., clay, slit, loam, gravel, snow, mud, or hard surfaces).
The undercarriage assembly components of track-type machines are subjected to severe operating environments. For example, debris, soil, rocks, etc. can enter the track and undercarriage of a track-type machine during operation. These abrasive materials can subsequently accumulate between the engaging surfaces of the undercarriage assembly components or drive equipment thereby causing wear. Further, undercarriage assembly components may be directly ground, worn, pitted, scratched or cracked by such debris, soil or rocks.
Also, due to the functional nature of the track-type machines, the undercarriage parts of these machines are required to be in intimate contact with wet sand, mud or corrosive materials, leading to corrosion. The corrosion cannot be eliminated by hardening the steel with surface treatments such as carburizing, nitriding or other conventional surface treatment methods because they are not cost effective against the high wear and corrosion environment that a track link faces during service. A more expensive material such as highly alloyed steel is generally not used because of increase costs.
A track that is adjusted too tight can increase friction and cause accelerated wear to undercarriage assembly components. On the other hand, a track that is too loose can allow drive sprocket teeth to jump links, especially in reverse, causing wear to undercarriage assembly components such as the sprocket teeth, track pin bushings, bottom rollers, etc.
Therefore, track chain links are subjected to severe wear, corrosion and stress. Wear is mainly caused by direct contact with undercarriage rollers and idlers which themselves are hardened. The wear rate is enhanced due to abrasive action of dirt, sand and other hard materials such as rocks, trapped between the link/idler and link/roller contact surfaces. The wear problem may be further exacerbated when the abrasive material is harder than even the hardened steels. Although wear of links can be mitigated by applying hard faces on the surface of the rail as suggested in U.S. Pat. Nos. 7,657,990 and 3,955,855, the costs associated to the hardfacing materials and processes prevent it from being widely used in practices, especially when surface area is large.